The present invention relates generally to the field of digital loop technology utilizing a hub structure and, more particularly, to the field of diagnosis and recovery using a hub in high performance digital loops such as, for example, those hubs seen in Fibre Channel systems.
The value of the digital loop in high performance systems such as Fibre Channel is without question. Moreover, the use of such a loop has proven to be enhanced through the use of a hub which serves as a central connection point for the loop. In such a configuration, the loop is said to be in the form of a “star”. Initial development of hubs saw what may be referred to as an unmanaged or “dumb” hub. As these terms indicate, such hubs served much in the manner of a patch panel, devoid of any monitoring capability as to the data passing through the hub.
Still considering the hub technology of the prior art, attention is now directed to FIG. 1 which illustrates a more recent digital system generally indicated by the reference numeral 10. System 10 includes a Fibre Channel hub 12 serving to interconnect a loop 14 including a plurality of stations S1-S4. System 10 further includes a local area network (LAN) 16 having independent connections 17a and 17b with stations S1 and S2, respectively. LAN 16 further includes a station S5 as well as a work station (WS) 18. Unlike the earlier generation of hubs described above, hub 12 includes limited diagnostic capabilities. These capabilities have generally been limited to high level observation of the data traveling around the loop. More specifically, these prior art diagnostic capabilities may indicate that certain packets of data are corrupted in addition to indicating the point of origination of the corrupted data. At first blush, this may seem to be extremely useful information for purposes of diagnosis. One must remember, however, that the corrupted data may have traveled through a substantial number of stations between it's point of origin and it's destination. For example, data originating from S2 and destined for S1 on the loop must intermediately pass through stations S3 and S4. Therefore, it is possible for the data to have been corrupted at any point along this path. An unsuspecting system administrator who immediately assumes that S2 is responsible for the corrupted data can waste enormous effort in attempting to diagnose a problem which may occur anywhere along the loop between S2 and S1.
Still referring to FIG. 1, in attempting to perform a detailed diagnosis, a technician may utilize a logic or protocol analyzer 20. S2 and hub 12 are originally connected using cable 22. The analyzer may be connected by disconnecting the original cable 22 at one end and then reconnecting the disconnected end to the analyzer such that original cable 22 is represented as a dashed line indicated by the reference number 22a and an additional cable 24 is used to connect the analyzer with S2. Assuming the problem is not being caused by S2, the technician has little hope of resolving the problem using the analyzer as depicted. Thus, the use of an analyzer in such a scenario is disadvantageous. Moreover, as another disadvantage, it is important to note that the use of the analyzer is intrusive. That is, connection of the analyzer itself modifies the structure of the loop. This fact can cause severe complications in some cases. For example, if the problem is being caused by a loose connector (not shown) at S3, connection of the analyzer may make the problem disappear if the output signal of the analyzer is greater than the output signal of S2 whereby to overcome attenuation being caused by the loose connector at S3. In this scenario, a reasonable technician may assume that the problem has somehow corrected itself, since the analyzer will indicate that there are no errors. Unfortunately, however, as soon as the original connections are restored, the masked problem will return. The technician is then likely to remain suspicious of S2, replacing it and its associated connections and is also likely to suspect fiber 22. As can be appreciated, this disadvantageous hit or miss technique is likely to be a long process. Moreover, each time a connection is disturbed to insert the analyzer, the loop is taken out of service. The process can also be expensive just due to replacement of any number of perfectly good, but suspect components.
Continuing to consider the use of an analyzer, it should also be appreciated that analyzer diagnosis is further complicated by the fact that the analyzer is generally configured to monitor only one or two points. This is an important consideration since the loop, unlike LAN 16, is not a broadcast medium. That is, the data present between different pairs of stations on loop 14 is itself different since the stations themselves insert and remove data from the loop. Just through the use of an analyzer, it is very difficult to gain a complete “picture” of what is going on in the loop which may, in fact, represent the only way in which a particular problem may be understood. Not only is the analyzer ineffective in many cases, it is also typically expensive. It is not uncommon for a Fibre Channel analyzer to cost $45,000.
The present invention provides a highly advantageous arrangement and associated method which resolves the foregoing disadvantages and difficulties while providing still further advantages, as will be seen hereinafter.